1. Field of the Invention
The present invention relates to a heat sink fan, and more particularly to a heat sink fan mounted on an electric component or an electric instrument such as an integrated circuit, for cooling the same.
2. Description of the Related Arts
A small heat sink fan is widely used for cooling an instrument which houses many electric parts, such as an OA instrument, a medical instrument or an experimental instrument. In FIGS. 1 and 2 is shown a small heat sink fan used as a heat generation preventing apparatus. As shown in these figures, a heat sink fan 1 is of an axial type and comprises an upper casing 2 having a rectangular shape as viewed from above, a lower casing or a heat sink 3 having a rectangular shape as viewed from above, and a fan motor 1A including a propeller-shaped impeller 4 and others.
The upper and lower casings 2 and 3 define a space in which the fan motor 1A rotates. A plurality of vents 5 for passing air are formed in the outer casing 2. Integral connection portions 7 each having a blind end are formed on the four corners of the outer casing 2 (FIG. 2). The lower casing 3 forming a heat sink comprises a blind bottom portion or a bottom portion 8 formed with a punched window of a circular shape or any other shape (not shown), heat dissipating fins 9 rising from the side edges of the bottom 8 and connecting portions 11 provided with projections 10 received in the respective blind holes 6 of the upper casing 2 and formed on the four corners of the lower casing 3.
The impeller 4 is provided with a cup-shaped rotating member 12, and a plurality of blades 13 projecting radially outward from the outer periphery of the cup-shaped rotating member 12. A rotary shaft 14 is rotatably supported in a cylindrical central inner sleeve of the upper casing 2 by means of bearings 15, and the lower end of the rotary shaft 14 is fitted in a central through hole of the cup-shaped rotating member 12. A rotor magnet 16 is fixed to the inner periphery of the cup-shaped rotating member 12 by means of a yoke 12a. The cup-shaped rotating member 12, the yoke 12a and the rotator magnet 16 constitute a rotor 17. On the inner boss of the outer casing 2 is mounted a stator 18 comprising a stator core having a plurality of teeth arranged circumferentially of the inner boss, and a coil wound around the teeth.
One casing must be disposed just over the other casing and fixed to the other casing by holding them in parallel and by adjusting them. Thus, the assembly requires special attention and skill.
When an electric instrument on which such a heat sink fan is mounted receives shocks during its movement, transportation or operation, the upper and lower casings are separated easily from each other to prevent the fan motor 1A from operating properly. Because the upper and lower casings are assembled together merely by tightly inserting projections into blind holes having the same diameter as the projections.
In order to solve these problems, the upper and lower casings may be fixed together by means of an adhesive, a screw or other fixing means. However, these means are not preferable, because processes and a number of parts increase. It is desired, therefore, that both casings be undetachably connected together rapidly and easily by very simple means without increasing processes and a number of parts.
In use, the lower casing 3 is placed at its bottom portion 8 on an electric part 20 such as a chip of an IC or LSI. An electric power is supplied to the fan motor 1A through electric wires 21 to rotate the fan motor 1A. Then, the impeller 4 rotates, and air is introduced in the lower casing 3 through the heat dissipating fins 9, cools the bottom 8 and is exhausted axially through the vents 5. In this way, most heat generated from the electric part 20 is dissipated.
As a fan motor has become miniaturized, however, the size of the heat sink fan which houses the fan motor has become smaller and smaller. This compactness reduces the surface area of the lower casing and deteriorates heat dissipating efficiency of the lower casing. If, therefore, heat is not dissipated securely, heat generated from the electric part is likely to give the electric part itself an adverse effect.